Machine for grinding gears



Nov. 23, 1937. E. w. BULLOCK ET AL 2,099,674

MACHINE FOR GRINDING GEARS Filed Nov. 6, 1934 15 Sheets-Sheetl @N Mm 3nventor6 ZCzZzZ/azwy, awfwwwm 6 fQ-Q w.

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MACHINE FOR GRINDING GEARS Fil ed Nov. 6, 1954 15 Sheets-Sheet 15 worm Patented Nov. 23, 1937 UNITED STATES MACHINE FOR GRINDING GEARS Edward W. Bullock, Clarence T. Galloway, Leonard O. Carlsen, and Robert S. Condon, Rochester, N. Y., assignors to Gleason Works, Rochester, N. Y., a corporation of New York Application November 6, 1934, Serial No. 751,738

35 Claims.

One object of the invention is to provide a spiral bevel and hypoid gear grinding machine of the dished wheel type that will be of improved design and simpler in construction than machines of this type previously built.

A further object of the invention is to provide a grinding machine in which separate means are provided for controlling the preliminary or rough grinding and the final or finish grinding operations and in which the means controlling the finish grinding operations is so constructed that a finer quality of finish will be obtained.

Still another object of the invention is to provide a grinding machine in which feed mechanism is located directly behind the part being fed whereby to reduce the mass of the parts being moved and to obtain a direct and steadier feed.

Still another object of the invention is to improve the accuracy of grinding by providing'a gear grinding machine in which the dressing mechanism is mounted on a relatively fixed part of the machine and the wheel is moved up to the dressing mechanism for dressing, thereby insuring that the wheel is always dressed in the same position and to the correct pressure angles.

A further object of the invention is to provide an improved and simplified mechanism for dressing simultaneously the two sides and the tip of a grinding wheel.

Still another object of the invention is to provide in a machine of the dished Wheel type, means whereby the gearing for producing the swing of the wheel can also be actuated at will to swing the wheel beyond its normal working path to bring it to dressing position.

A further object of the invention is to provide mechanism for quickly clamping the grinding wheel head at a plurality of points simultaneously or for releasing the same, and in this, as in certain other aspects, the invention has utility in connection with gear cutting as well as gear grinding machinery and in connection with machine tools generally.

A further object of the invention is to provide in a machine tool, a unitary control for the chucking mechanism, the mechanism for movingthe workhead to and from. operative position, and the mechanism for clamping the workhead in operative position. In this connection, a further object of the invention is to provide means which will safeguard the operator of the machine and insure that the work is chucked to his satisfaction before the workhead can be moved to operative position. Still further, means is provided that insures that the workhead is actually in operative position before it is clamped.

Still another object of the invention is to provide a machine in which the grinding wheel is dressed automatically at the end of each grinding cycle as, for instance, at the ends of both the rough and finishing grinding operations.

Still another object of the invention is to provide a machine in which the grinding wheel will be advanced automatically relative to the work after each dressing operation to compensate for wheel-wear. In this connection, a further ob ject of the invention is to provide means for automatically clamping and unclamping the grinding wheel head prior to and after, respectively, advancement of the wheel.

A still further object of the invention is to provide means operative at the end of roughgrinding for automatically shifting the means that controls the feed during rough-grinding out of operative position and bringing the means that controls the feed during the finishing grinding into operative position.

A still further object of the invention is to provide a machine having means for automatically releasing the workhead and for moving the workhead from operative position to chucking position when the operations on the work have been completed and for dechucking the completed work piece during the latter movement.

Further, it is an object of this invention to combine the various automatic features described in a single machine so as to provide a gear grinding machine which will be fully automatic in operation and which will require no attention from the operator whatsoever from the time the machine is started until the work on the gear has been completed and the gear dechucked.

The invention also includes various other improvements and refinements having to do with the production of machinery for producing gears, all of which will appear clearly from the following description and from the appended claims when read in conjunction with the accompanying drawings.

Two different embodiments of the invention have been illustrated in the drawings, one a machine which is semi-automatic in operation and the other a machine which is fully automatic.

In the drawings:

Fig. 1 is a side elevation, with parts broken away, of a semi-automatic machine for grinding spiral bevel and hypoid gears;

Fig. 2 is a vertical sectional View on an'enlarged scale taken longitudinally through the grinding-wheel head;

Fig. 3 is an elevational view of the wheel head, looking at the grinding wheel and dressing mechanism;

Fig. 4 is a fragmentary vertical sectional view through the tool end of the machine and taken at right angles to the view of Fig. 2;

Fig. 5 is a fragmentary view showing details of the grinding wheel oscillating mechanism and parts of other drives of the machine, the view being a sectional view taken approximately on the line 55 of Fig. 4;

Fig. 6is a plan view of the tool head, the view being on a somewhat reduced scale and parts being broken away;

Fig. 7 is a transverse vertical sectional view through the workhead of the machine on an enlarged scale;

Fig. 8 is a view of the workhead clamp taken at right angles to the view of this clamp seen in Fig. 7;

Fig. 9 is a rear end view of the workhead showing details of the index mechanism;

Fig. 10 is the section on theline lit-l0 of Fig. 9;

Fig. 11 is a diagrammatic view showing the connection between the rotary control valve, the chucking mechanism, the mechanism for moving the workhead, and the mechanism for clamping the workhead, all of which mechanisms are controlled by said valve;

Fig. 12 is a side elevation of the stop-plate for controlling the movement of the control-valve;

Figs. 13 to 16 inclusive are diagrammatic views illustrating the operation of the control-valve;

Fig. 17 is a development of the rotary part of this valve;

Figs. 18 and 19 are developments of the feedcams controlling the rough and finish grinding operations, respectively; I

Fig. 20 is an enlarged plan view of the feed cam and follower;'

Figs. 21 and 22 are views of the dressing mechanism, partly in section, and taken at right angles to one another; Fig. 22 showing, also, diagrammatically the connection between the dresser control valve and the dressing mechanism;

Figs. 23 and 24 are plan sectional views, showing two different positions of the dressing mechanism in the act of dressing a grinding wheel;

' Fig. 25 is a section on the line 25-25 of Fig. 4;

Fig. 26 is a partial plan view corresponding to Fig. 6 but on a'somewhat enlarged scale, showing the wheel-head of a modified form of machine constructed to be fully automatic in operation;

Fig. 2'7 is a sectional View of the control-valve used in the fully automatic machine for controlling the chucking operation, the movement of the workhead, and the clamping of the workhead, and showing the mechanism for operating this valve;

Fig. 28 is a side elevation of the stop-plate for controlling the movement of this valve;

Fig. 29 is a fragmentary sectional view of the line 29 29 of Fig. 26;

Fig. 30 is a fragmentary sectional view on the line 30-30 of Fig. 26;

Fig. 31 is a fragmentary sectional view on the line 3i-3l of Fig. 26;

Fig. 32 is a section on the line 32-32 of Fig. 26;

Fig. 33 is a fragmentary sectional view, showing the two needle valves that control the rate of dressing of the grinding wheel prior to roughgrinding and prior to finish grinding, respectively;

Figs. 34 and 35 are views showing two different positions of the cycle-control-bar at two different stages in the operation of the fully automatic machine; and

Fig. 36 is a diagrammatic view of the electrical and hydraulic circuits of the fully automatic machine and illustrating the method of operation of this machine.

The advantages of a rotating and swinging tooth surface or surfaces being ground. The

present invention constitutes in several respects an improvement over the Taylor patent as will now be described.

In the machines illustrated, the gear is held stationary during grinding and the grinding of the tooth surfaces for their full height is effected by feeding the rotating and swinging grinding wheel into the gear until full depth position is reached. One side of a tooth space may be ground at a time, but preferably both sides of the tooth space will be ground simultaneously. When a tooth surface or a pair of tooth surfaces have been ground, the wheel is withdrawn and then the gear is indexed. The alternate feed and withdrawal continues until the gear is completed.

To secure the best possible results as regards quality of finish of the tooth surfaces ground, we have provided separate feed cams for the rough and finish grinding operations. The two cams are mounted upon the same shaft and this shaft is shiftable axially to bring the cams alternately into operative position. The roughing cam is so constructed as to provide a continuous feed during grinding and stock is removed throughout the whole of the feeding movement and as soon as the wheel reaches full depth position it is withdrawn. The finishing cam is constructed, however, to produce a dwell of the grinding wheel in full depth position at the end of the feed movement. This dwell insures cleaning up of the tooth surfaces and a smooth tooth surface finish. The finishing cam, moreover, is designed to produce a finer feed than the roughing cam and in this way, also, conduces to a better quality of tooth surface finish.

A further feature of the invention, which also makes for improved quality, is the mounting of the cams themselves. The grinding wheel is journaled in an oscillating carrier which is oscillated to produce the longitudinal swinging motion of the wheel. This carrier is journaled in spaced hearings in the wheel head and the feed-cam shaft is mounted in the head to extend between these bearings so that the feed-cams operate directly behind the wheel and substantially in line therewith. With this construction, the mass being moved during feed is reduced and a steadier feed movement is obtained.

The wheel head is adjustable axially of the swinging carrier to compensate for wear of the wheel. One of the constructional features of the present machine and one having general application is the mechanism for clamping the wheel head to the frame after adjustment. In the machines shown, the clamping mechanism includes four T-bolts that engage the frame at four spaced points. Each of the T-bolts is secured to a piston that is movable in a cylinder bored in the wheel head and the four pistons are controlled from a single centrally located valve. Thus the head can be clamped or released simultaneously at four different points by operation of this single control valve. This very much expedites handling of the machine.

The dressing mechanism itself is also novel. Three diamonds are employed, two for dressing opposite sides of the wheel and the third for dressing the tip of the wheel. One of the side dressers is mounted upon the head of a hydraulically-actuated piston-rod. The end or tip dresser is mounted upon a swinging arm and this arm carries a follower that engages a cam-projection on the head of the piston-rod so that as the first-mentioned side dresser moves back and forth under actuation of its piston. the tip dresser is swung back and forth to dress the tip of the wheel. The other side dresser is also mounted upon a swinging arm and this latter swinging arm carries a follower that engages a cam-projection upon the first mentioned swinging arm,

angular adjustments of the side dressers permit setting them to dress the opposite sides of the grinding wheel to any desired pressure angles. The tip dresser is longitudinally adjustable on its arm so that the grinding wheel may be dressed to any desired point-width. The drum itself is laterally adjustable-on the wheel-head and this adjustment is in a direction radial of the axis of swing of the grinding wheel so that the diamonds can be adjusted to dress wheels of difierent diameters.

To dress the grinding wheel, it is swung up out of its normal operating path to bring it into operative relation with the dressing diamonds which are, as described, relatively fixed. The train of gearing for oscillating the wheel carrier includes a differential and the housing of this differential is held stationary during grinding. To swing the grinding wheel to or from dressing position, a hydraulically-operated piston is actuated. This piston is connected to a rack that is adapted to rotate the housing on actuation of the piston. Adjustment of the rack relative to the piston allows of positioning the grinding wheel to grind gears of different spiral angles. but the wheel is always moved to the same position for dressing regardless of its spiral angle adjustment.

The indexing mechanism of the machine illustrated is of the notched plate type and is actuated from a cam that is driven in timed relation with the feed cam shaft.

In order to place a gear on the machine or remove a gear after it has been ground, the workhead is moved to loading position. The movement of the workhead to and from loading position, the clamping of the workhead in operative position, and the chucking and dechucking of gears upon the work spindle are controlled from a single rotary valve. This valve controls a pston that moves the workhead to and from loading position, a piston that actuates or releases the workhead clamp, and a piston that controls the operation of the chucking mechanism.

On both the semi-automatic and the fully automatic machines, the rotary valve just described is manually operable in one direction to first chuck a gear on the work spindle, then move the workhead into operative position, and then clamp the workhead in operative position. A stop or cam-plate is provided in conjunction with the valve just described to insure that the operator will take a positive. action between chucking and movement of the workhead to operative position and between movement of the workhead to operative position and clamping of the workhead. This insures that the operator will have the gear properly lined up with the grinding wheel before he moves the workhead into operative position and it also insures that the workhead will have fully reached operativeposition before it is clamped.

In the return movement of the control valve, the workhead is released, then moved to loading position and the completed gear is dechucked. The steps take place automatically in the fully automatic machine, after the gear is completely ground.

In the machines illustrated, the work spindle is journaled in a slide that is verticallv adjustable upon the workhead or column and the workhead or column slides on a base that is angularly adjustable upon a plate. The plate is in turn laterally adjustable upon the frame of the machine. The vertical and lateral adjustments permit of adjusting the gear relative to the grinding wheel for spiral angle. The angular adjustment is for the purpose of adjusting the gear in accordance with its pitch cone angle.

In the semi-automatic machine, a shift from the roughing to the finishing feed cams and vice versa is effected manually by reciprocation of a sleeve in which the cam shaft is journaled and a wedge is provided for. holding this sleeve against movement when the finishing cam is in operative position so as to eliminate all possibility of vibration during the finish grinding operation. The movement of the grinding wheel to and from dressing position is also effected manually as are. also, the advance of the grinding wheel head after dressin to compensate for wear and the operation of the valve that controls the T-bolts for clamping this head. The rotary valve that controls chucking movement of the workhead to and from loading position and clamping or releasing of the workhead. in the semi-automatic machineis manually operable in both directions. In this machine. the dressers are also manually controlled, a manually operable valve being provided for controlling the movement of the piston that actuates the dressers.

In the fully automatic machine the various operations described are automatic. This machine stops with the workhead at loading position. the work dechucked and the grinding wheel swung up to dressing position. When the machine is started, the grinding wheel is automatically swung down into grinding position. This closes a contact that starts the main drive motor. The operator then manually rotates the con rol valve to chuck a gear, move the workhead into operative position and clamp the head in this posi tion. The machine then goes through the rough grinding cycle. the grinding wheel being fed into the gear to grind a tooth space of the gear and being then withdrawn and the gear being then indexed and so on until all of the tooth surfaces of the gear have been ground. The automatic stop mechanism of the machine then operates to stop the main drive motor and cause the grinding wheel to be again swung up to dressing position. When the grinding wheel reaches dressing position, a contact is made that shifts the roughing cam out of operative position and brings the finishing feed cam into operative position. The wheel head is then automatically unclamped and fed forward a distance .equal to the amount of stock to be removed from the grinding wheel in the dressing operation. At the end of this advancing movement of the wheel head, a valve is shifted that controls the dressing mechanism and the dressing mechanism goes through its cycle to dress the grinding wheel. At the completion of the dressing operation, the grinding wheel is automatically returned to grinding position and the machine then goes through its finish grinding cycle. The wheel is alternately fed into the gear to finish grind each tooth space, and withdrawn and during the periods of withdrawal, the gear indexed. When all of the teeth have been finish ground, the automatic stop mechanism again trips to swing the grinding wheel up to dressing position and the shaft carrying the feed cams is again shifted axially. The grinding wheel head is unclamped and advanced and the wheel is dressed, as before. The shift of the feed cam shaft at this time, however, will break the starting circuit to the machine so that the completion of the dressing operation will not cause the wheel to be again swung down into operative position. This shifting movement of the cam shaft will also release the rotary control valve. This valve will then be rotated automatically under actuation of a spring to automatically release the workhead, move it to loading position and dechuck the gear. Thus the whole operation of the machine takes place automatically, without requiring any attendance of an operator, from the time that the machine is started and the gear is chucked until the gear is completed both rough and finish ground, moved to loading position and dechucked.

The principal features of the invention and the method of operation of the machines shown in the accompanying drawings have been described in general terms. Reference will now be had to the drawings for a more detailed description of the invention and of these machines.

The semi-automatic machine will be described first.

30 designates the base or frame of this machine and 3| (Figs. 1 and 2) designates a housing or upright which is rigidly secured to this frame at one end thereof and which may be integral therewith. This housing or upright 3| is hollowand is formed with plane top surfaces on which there slides a wheel-head 3!.

Mounting for the grinding wheel Mounted in the wheel-head 33 is an oscillatable and slidable wheel-carrier or quill 34. wheel-carrier or quill 34 is of irregular shape as will be clear from Fig. 2 of the drawings.

The column or upright 3| is formed at its forward end with a cylindrical bearing 35 (Figs. 2 and 3). There is a cylindrical plate or guide 36 secured to the quill 34 at the front end thereof by screws 31. This plate 36 has its bearing in the bearing 35 of the column 3| and forms a guide for the quill 34 in its oscillatory and sliding movements.

There is a sleeve 39 secured in an opening in This the rear end of the quill 34 by screws 39. This sleeve is mounted for rotating and sliding move- 'ments in a bearing formed in an arm 49 that is integral with the plate or wheel-head 32 and depends therefrom.

There is a ball-thrust bearing 42 mounted in the quill 34 directly behind the cylindrical driveplate 36. There is a sleeve 43 mounted in this bearing and formed at its rear end with a flange 44 that seats against the rear face of the bearing. A cam-follower or projection 45 (Figs. 2 and 20) is secured to this flange by screws 46.

Pending from the plate or wheel-head 32, adjacent its forward end is a hollow hearing or arm 56 (Figs. 2 and 4). This arm 50 is formed at its lower end with a semi-cylindrical seat or bearing 49 (Fig. 4). This bearing 49 aligns with the bore of the sleeve 43 already referred to. Mounted in the bearing 49 and the sleeve 43 is a sleeve This sleeve 5| is held in the bearing 49 by a cap-member 54 and is secured against axial movement relative to the arm 59' by a pin 52 and a screw 53 that are mounted in a cap-member 54 and engaged in the sleeve. The cap-member 54 is secured to the depending bearing 50 by bolts 55. The sleeve 5| carries a key 56 that engages in an elongated key-way 51 that is formed internally in the sleeve 43. Thus the sleeve 43 is held against rotation relative to the sleeve 5| while relative sliding movement between the two sleeves is permitted.

69 designates a plate which is secured to the quill 34. This plate has a forwardly projectihg stem or stud 6| that is journaled on bearings 62 in the sleeve 5|. The forward end of this stud 6| is of reduced diameter and is mounted in a thrust-bearing 63 that is slidably mounted in the sleeve 5|. A nipple 64 is threaded in the forward end of the sleeve 5| and between this nipple and the bearing 63 there is interposed a coil spring 65. 1

Journaled in the quill 34 is a wheel-spindle 19 which is tapered at its forward end to receive the adaptor 1|. The cupped grinding-wheeel W used on the machine is secured to the adaptor by nuts 12 and the adaptor is secured to the spindle III by threading up on the nut 13 which threads on the end of the wheel-spindle. The wheelspindle I0 is journaled on anti-friction bearings 14 and 15 in a sleeve 16 that is secured to the quill 34 by bolts 18. The usual labyrinth-seal TI is provided at the forward end of the spindle to prevent entry of dirt or grit into the bearings.

Drive to the grinding wheel The grinding-wheel spindle III is driven from a motor (not shown) that is mounted in the base or frame of the machine. The drive is from the motor through a belt 66 to a pulley 8| that is keyed to a hollow-shaft 82 which is journaled on anti-friction bearings 63 and 84 in an endplate 85 which is secured by screws 86 to the upright or housing 3|. The belt 90 and pulley 8| are protected by a guard 91 which is secured to the housing 3| in any suitable manner.

Journaled on antifriction bearings 99 and 9| in the sleeve 36 is a shaft 93 which has a telescoping splined connection with the hollow shaft 32. Keyed to the shaft 92 is a bevel gear 93 that meshes with a bevel gear 94. The gear 94 is keyed to a shaft 95 which is Journaled on antifriction bearings 96 and 91 in a sleeve 96 that is fixedly secured in the quill 34.

Keyed to the shaft 95 at its forward end is a pulley I96. This pulley drives a pulley Ill Gil through a belt I 02. The pulley I III is keyed to the rear end of the wheel-spindle 10.

Through the gearing just described, a rotary motion is imparted to the grinding-wheel to produce the grinding action. We shall now describe the mechanism for producing the swinging motion of the grinding wheel required to move the wheel longitudinally along the tooth surfaces to be ground to grind the tooth surfaces from end to end.

Wheel oscillating mechanism Mounted in the base or frame of the machine is a motor I05, (Fig. 1). This drives a vertical shaft I06 through a suitable coupling I01. The shaft I06 carries at its upper end a bevel pinion I08 that meshes with a bevel gear I09 secured to a shaft H0. The shaft IIO has a spur gear II2 fastened to it at its outer end. This spur gear meshes with a spur gear I I3 (Figs. 1 and which is splined to a shaft H4. The shaft H4 is journaled on anti-friction bearings H5 in the column 3| and a bevel pinion H6 is keyed to the shaft at its inner end. This pinion meshes with a bevel gear II1 which is secured by screws II8 to a crank-plate I20. The crank-plate is integral with a shaft I2I that is journaled on anti-friction bearings I22 and I23 in the column 3I. The crank-plate is of the usual construction and is formed with a crank-plate slot I24 (Figs. 4 and 5) which receives the adjustable block I25 that carries the crank-pin I26. The crank-pin I26 is connected by a rod I21 to a pin I28 which is secured by a nut I29 in a link I30. The rod I21 is secured to the crank-pin I26 by a nut I3I.

The link I30 is connected to a shaft I32 and is held thereon by the nut I33. This shaft is journaled on anti-friction bearings I35 and I36 in the sleeve I31 of a differential-housing I38.

The shaft I32 is integral with one of the side gears I40 of the differential. This gear I40 meshes, with the planetary-gears HI and I42 which are journaled on anti-friction bearings I43 and I44, respectively, in the differential housing, and are also mounted upon the differential-spider I45. The planetary-gears MI and I 42 mesh with a differential side gear I46. This gear I46 is integral with a shaft I41 that is journaled on antifriction bearings I48 and I49 in a sleeve I50 that is integral with the differential housing. The sleeves I36 and I50 of the differential housing are journaled in bearings I5I and I52, respectively, that are formed integral with the column or housing 3|.

There is a spur gear I55 keyed to the shaft I41 at its rear end and this spur gear meshes with a spur gear segment I56 (Figs. 4 and 2) that is integral with the quill 34.

Through the gearing just described, then, an oscillating motion is imparted to the quill and through the quill to the grinding wheel to swing the grinding wheel back and forth along the length of the gear teeth being ground. We shall next describe the mechanism for imparting to the grinding wheel its alternate movements of feed and withdrawal.

Wheel feed mechanism Mounted on the shaft II4 already referred to (Figs. 1 and 5) and splined thereto is a spur gear I60 that meshes with a spur gear I6I which is keyed to a stub-shaft I62. This shaft is journaled on anti-friction bearings I63'and I64 in a quadrant I 65 that is secured to the housing or upright 3i by a bolt I66.

The spur gear I6! meshes not only with the spur pinion I60 but also with a spur gear I68 (Fig. 1) which is secured to a shaft I69 that is journaled in the column 3I and which has fastened thereto a bevel gear I10. This bevel gear meshes with a bevel gear I12 (Figs. 1 and 5) that is keyed to a shaft I13. This shaft I13 is journaled on anti-friction bearings I14 and I15 in the column 3|.? At its forward end, the shaft I13 has a sliding splined engagement with a sleeve I11 that is journaled on anti-friction bearings I18 and I19 in the column 3I. A bevel gear I8!) is keyed to the sleeve I11 and meshes with a bevel gear I8I that is keyed to a vertical shaft I82 that is suitably journaled in the column 3I.

This vertical shaft I82 has secured to its upper end a bevel gear I84 (Fig. 6) which meshes with a bevel gear I85 that is secured to a horizontal shaft I86. The shaft I86 carries at its inner end a bevel pinion I81 which meshes with a bevel gear I88 (Figs. 6 and 2). The bevel gear I88 is keyed to a sleeve I89 that is journaled on anti-friction bearings I9I and I92 in a bracket I93. This bracket is suitably secured to the upper face of the wheel-head 32 and the horizontal shaft I86 is journaled in this bracket.

The sleeve I89 has splined engagement with a vertical cam-shaft I95 that is journaled on anti-friction bearings I96 and I91 (Fig. 2) in a sleeve I98 which is vertically reciprocable in the cylindrical bore of the depending arm 50 already referred to.

There is a cam-member 200 fixedly secured to the lower end of theshaft I95. This cam-member is provided with two peripheral cam-tracks 20I and 202 (see Figs. 18 and 19). One of these tracks is a roughing-cam track and the other a finishing-cam track. They are adapted to be engaged selectively with the projection or follower 45 to impart feed movement to the quill 34 and the grinding wheel.-

To bring either cam-track into engagement with the follower 45, the sleeve I98 is moved vertically. To this end a handle or crank 205 (Fig. 1) is provided. This is secured to a shaft 206 that is journaled in the plate or head 32 and that carries at its inner end a spur pinion 201 (Fig. 2). This pinion meshes with a rack 208 out into the peripheral surface of the sleeve I98 adjacent to the upper end thereof.

The sleeve I98 is provided adjacent to its lower end and at a point diametrically opposite the rack 208, with a slot 2I0 that extends from its lower end upwardly and tapers outwardly. This slot receives a tapered key 2 which is adjustably secured in the arm 50 by means of bolts 2I2. These bolts pass through an elongated slot 2I3 in the arm 50 and thread into the key 2I I. The

key 2II operates to hold the sleeve I98 against 'rotation and, in the lower position of the sleeve,

when the finishing cam 2I0 is engaged with the follower 45, acts as a wedge to hold the sleeve rigidly against vibration, thereby to insure a perfect finish in the finish-grinding operation.

A lay-out of the track of the roughing cam is shown in Fig. 18. In the rotation of this cam, the quill 34 is first fed at a rapid rate toward the work, but when the grinding wheel reaches the position where it contacts with the gear, the rate of feed is reduced and the wheel is fed on into full depth engagement with the gear at a much slower rate. The slow-feed prevents an excessive burden from being placed on the wheel and produces a rough-finish on the sides of the teeth at the end of the rough-grinding operation that will 

